Heat exchanger construction



Dec.'l6, 1958 E. BRUEGGER x-:T AL -2,864,404

HEAT EXCHANGER CONSTRUCTION 5 Sheets-Sheet 2 Filed Sept. 15,. 1953 uw Bm Hem m B W Q m7 w. s \|1/ mrs T 3 Q B'M, A L nP M av 5 Sheets-Sheet 3E. BRUEGGER ETAL HEAT EXCHANGER CONSTRUCTION Dec. 16, 1958 Filed Sept.15, 1953 EMSVKZTORM BY Phigmszgen gzew ATTRNEYS Dec. 16, 1958 E.BRUEGGER HAL 2,864,404

HEAT ExcHANGER CONSTRUCTION Filed sept. 15, 195:5 5 sheets-sheetA E tlI( V EN TORS .ribes rule el' Phizif ge d MAL mm NN.

Amm

Dec. 16, 1958 E. BRUEGGER ET AL 2,864,404

HEAT EXCHANGER CONSTRUCTION 5 Sheets-Sheet 5 Filed Sept. 15, 1953INVENTORS Ernesirwegg'er Pklzfp S. ezz d MT ATmRNEYS Unite States HEATEXCHANGER CONSTRUCTION Application September 1S, 1953, Serial No.380,214

1 Claim. (Cl. 13S-38) The invention relates to heat exchangers such assteam generators, super heaters, etc., and to methods of making thesame, and has particular significance in connection with heat exchangersof the shell and tube type in which a tube bundle Yis enclosed within agenerally cylindrical shell, and the ends of the tubes of the bundle aresecured in one or more tube sheets connected to the shell of the heatexchanger, and each of the tubes is a double walled tube with a leakagedetector space provided between the two tubes to prevent-if failure ofeither of the tubes occurs-intermixing of for example, heated andheating or cooled and cooling liquids passed through and around thetubes, and also to provide means for detecting a leak in any of thetubes.

It has been known in the past to provide heat exchangers, such assurface coolers handling a primary medium to be cooled and a secondarycooling medium, with means for circulating the different mediums throughand about a double walled tube comprising inner and outer tubes. Suchtubes have been arranged to have surface to surface contact with aplurality of relatively large longitudinal passages or grooves formedbetween the two tubes communicating with a leakage detector compartmentso as to convey fluids leaking through one of the tubes on failurethereof to the detector compartment to provide a visual indication ofany such leakage. The double walled tube prevents intermixing of thecooled and cooling or heated and heating mediums if one of the inner orouter tubes fails due say to corrosion or the like.

In fabricating such double walled tubes the grooves ordinarily have beenformed longitudinally in the inside surface of the outer tube, thegrooves being relatively large and `few in number; and the tubesnormally have been relatively small in diameter. In order to providesuch grooves in the interior surface of the outer tube, such outer tubesusually have been made as an extruded product which has required the useof a soft metal or a soft metal alloy in order to form such a tube as anextrusion.

Sometimes the longitudinal internal grooves in the outer tube have beenformed by a broaching operation rather than by forming the grooved tubesas an extrusion. Sometimes instead of forming the grooves in the insidesurface of the outer tubes, the grooves have been formed longitudinallyin the exterior surface of the inner tubes but here again unless suchtube is formed as an extrusion difficulty has been encountered informing such grooves in a thin walled small diameter tube ofconsiderable length without weakening the tube walls or in thealternative making the tube wall sulliciently thick to avoid collapse informing the grooves or when the tube is subjected to high pressureoperation.

As a practical matter, the manufacture of the grooved tube has beenlimited to the use of soft metal, and to forming the same as anextrusion product with the grooves in the interior of the outer tube.These practical requirements involve the further disadvantage, inaddition to the limitation ofthe soft metals or alloys which must atentO be used, that the manufacture of such extruded tubes is veryexcessively expensive.

These diiculties, disadvantages and limitations created an extraordinaryproblem in the construction 0f double walled leakage detector tubes foruse in heat exchangers where high pressures, or high temperatures, orthe charac; ter of the medium being circulated through or around thetubes, has required the use of tubes formed of other than soft metalthat is a corrosion resistant metal such as stainless steel or nickelfor both the inner and outer tubes or stainless steel for one and nickelfor the other of the inner and outer tubes. Thin Walled small diametertubes of considerable length cannot be formed as a practical matter asan extruded product from stainless steel or nickel. Prior to thediscoveries of the present invention the cost of forming grooves byother means in either the inner or outer tube walls, or the cost ofincreased metal for thick walled tubes and the additional weightthereof, or combinations of these diiculties have prohibited themanufacture of double walled leakage detector tubes of stainless steelor nickel or combinations of the same.

Equipment using materials requiring the use of stainless steel or nickeltubes may have a low boiling point metal, or a low vapor pressure metalin molten state, or a molten salt, passed through the inner tube as aheating medium; and water to be converted into steam, or steam to besuperheated, may be passed through the heat exchanger shell in heatexchange relation through the double tube walls with the heating mediumfor being heated.

As compared With soft metals or alloys both stainless steel and nickelhave poor heat conductivity. Therefore it is most important when usingstainless steel or nickel to have as large an area of metal to metalcontact as possible between the inner and outer tubes for obtainingmaximum heat exchange through the tube walls. Thus the size of thegrooves which normally can be formed in an extruded product, must bematerially reduced when using stainless steel or nickel in order toprovide nearly complete metal to metal contact between the' exteriorsurface of the inner tube and the interior surface of the outer tube.Heretofore there has been no known way of forming grooves a fewthousandths of an inch in depth or width, satisfactorily in a surface ofa small diameter, thin walled stainless steel or nickel tube and suchtube could not be formed as an extrusion.

In other prior art constructions, double walled or bimetal tubes havebeen made of steel and copper or brass for use in refrigeratingequipment handling ammonia vapors. Difficulties were experienced in tubefailure apparently due to gas formation at the interface of the twometals forming the double Walled or bimetal tube. This difficulty wasobviated by providing shallow grooves in the surfaces of one of thetubes to convey any gas that may be formed away from the tube interfacesto prevent impairment of heat transfer and tube failure. The grooves insuch tubes normally have been formed by a breaching or similar operationwhich again is not adapted for the manufacture of double walled tubes ofstainless steel or nickel for some of the same reasons and because ofsome of the ditliculties encountered as hereinabove discussed.

It is an object of the present invention to provide a simple andinexpensive structure for overcoming 'the above mentioned difliculties.

Another object of the invention is to provide a double walled heatexchanger tube provided with leakage detection means in `which the innerand outer tubes are formed of stainless steel or nickel or lcombinationsthereof for handling corrosive fluids at high temperatures or pressures.

Another object of the invention is to provide a double walled leakagedetector heat exchanger tube which has maximum metal-to-metal contactbetween the concentric tubes.

Another object of the invention is to provide a double walled leakagedetector heat exchanger tube utilizing thinner walled tubes than in`structures made in accordance with the prior art.

Anotherobject of the invention is to provide concentric double conduittube arrangements with leakage de tector passages between the conduitsand characterized yby greater ease of manufacture and a greater varietyof metals which can be used for the inner and outer conduits.

Another object `of the invention is to provide a double walled leakagedetector heat exchanger tube in which it is not necessary to userelatively soft metal for one or both of the concentric tubes.

Another object of the invention is to provide double walled tubes yofthis type which are lighter in weight and characterized by asaving incost proportional to the expense of materials used.

Another object of the invention is to provide do'ublc walled leakagedetector heat exchanger tubes for use at higher temperatures and withmore corrosive `fluids than prior art double walled tubes.

A further object of the present invention is to provide an improvedmethod of providing leakage detector grooves in double walled tubestructures comprising -inner and outer tubes having thinner walls andformed of -a greater variety of metals than possible with priorprocedures.

These and other objects and advantages apparent to those skilled in theart from the following description and claim, may be obtained, thestated results achieved, and the described difficulties overcome by themethods, steps, procedures, products, articles of manufacture,constructions, combinations, sub-combinations, parts and elements whichcomprise the present invention, the nature of which are set forth in thefollowing general statements, pre ferred embodiments ofwhich-illustrative of the best modes in` which applicants havecontemplated applying the principles-are set forth in the followingdescription and shown in the drawings, and which are particularly anddistinctly pointed out and set forth in the appended claim forming parthereof.

The nature of one aspect of the discoveries and improvements of thepresent invention may be stated in general terms as preferably includingin a method of making a double walled leakage detector tube and shellheat exchanger construction particularly adapted for handling hightemperature extremely corrosive iluids, the

steps of providingseparate inner `and outer conduits or tubes ofcorrosion-resistant metal such as stainless steel or nickel,'formingsuch tubes as small diameter, relatively thinwalled, tubes such as saywith a tube wall of the order of one-sixteenth inch thick, forming alarge number of longitudinal grooves having a width or depth of theorder of -a few thousandths of-an inch in the outer surface of the innertube by rotating the tube on its axis and forcing an axially ribbed,rotatable, relatively axially short, grooving roll radially against theouter surface of the tube while advancing the roll longitudinally of therotating tube with the tube and roll axes parallel, to iron groovedportions complementary to the -roll ribs in the outer surface of thetube in a `helical path about the tube outer surface; co-ordinating andcontrolling the rate of roll advance and the length and spacing of theroll ribs such that when the tube makes one revolution the grooveportions formed in the helical path are `aligned with the grooveportions formed in such path during the previous revolution of the tube,so that when the roll has advanced from adjacent one end to adjacent theother end of the tube a series of continuous longitudinal grooves areformed in the outer surface of the tube; then telescoping the groovedtube with its longitudinally grooved portion within the outer tube andexpanding the inner tube slightly within the outer tube to seat thegrooved surface in intimate metal to metal contact between the grooveswithin the outer tube; then securing the ends of the inner and outertubes within spaced tube sheets with the grooves communicating with acompartment between Such tube sheets. v

The nature of another aspect of the discoveries and improvements of thepresent invention may be stated in general terms as including in heatexchanger construction of either the bowed tube or bayonet tube type,double walled tubes composed of inner and outer tubes, the ends of theinner tubes being secured in a tube sheet communicating with onecompartment, the ends of the outer tube being fixed in a second tubesheet spaced from the first tube sheet communicating with anothercompartment, there being a series of longitudinal grooves formed in theouter surface of that portion of the inner tube within the outer tube,said grooves communicating with said second compartment 'between saidspaced tube sheets, the outer tubes having a relatively small diameterof the order of three-fourths inch outside diameter, the inner and outertubes having a wall thickness of the order of one-sixteenth inch thick,the tubes being formed of metal or alloys such as stainless steel ornickel, and the grooves having Irelatively small depth and width of theorder of a few thousandths of an inch, whereby intimate surface tosurface contact between the grooves is obtained when a grooved innertube is telescoped and expanded within an outer tube while providingpassages through the grooves between the tubes for the detection offailure or leakage of either of the tubes.

By way of example, preferred embodiments of our improved heat exchangerconstruction and of improved parts thereof and of methods of making thesame, are illustrated in the accompanying drawings, in which;

Fig. 1 is a horizontal sectional View of a heat exchanger of the bowedtube type having concentric conduits or double walled tubes and aleakage detector system constructed in accordance with the invention;

Fig. 2 is a vertical sectional view of the heat exchanger shown in Fig.l;

Fig. 3 is an end view looking at the left end of thc heat exchangershown in Figs. l and 2;

Fig. 4 is a cross sectional view taken along the line 4 4 of Fig. 2;

eFig. 5 is a fragmentary enlarged vertical section adjacent the bottomof the left end leakage detector space as seen in Fig. 2;

Fig. 6 is an enlarged somewhat diagrammatic cross sectional view takenon the line 6 6 of Fig. 5;

Fig. 7 is a View in perspective showing the inner tube of Fig. 6 duringone step of its manufacture in accordance with a preferred method of theinvention;

Fig. 7a is a view similar to Fig. 7 showing a variation -in the methodof groove forming;

Fig. 8 is a vertical sectional view showing another form of heatexchanger constructed in accordance with the invention; and

Fig. 9 is a cross sectional view taken on the line 9 9 of Fig. 8.

Similar numerals refer to similar parts throughout the several views ofthe drawings.

Referring to Figs. 1 and 2, we have shown a high temperature, highpressure heat exchanger adapted for use with very highly corrosivefluids and comprising two similar spaced apart headers indicatedgenerally at 10 and 10', respectively.

Headers 10 and 10' are identical except opposite hand. For simplicityonly the left hand header 10 is fully shown, and it comprises a headbarrel portion 11 and a head cover 12 with the head cover secured as bybolts 13 to a ange portion 14 of the head barrel. The head barrel issecured as by an annular Weld 15 with an annular tube sheet 16 whichwill hereinafter be referred to as the outer tube sheet. An inner tubesheet 17 is located in spaced relation with respect to outer tube sheet16 by a ring barrel 18 which, as hereafter more` fully explained, formswith the tube sheets, a leakage detector space l19.

The side of the inner tube sheet 17 opposite the chamber 19 is securedas by a-n annular weld 20 with a somewhat conically shaped section 21,the opposite end of which is secured by weld 22 with the exchanger shell23 extending between the -two headers and two sets of tube sheets. Theheader and tube sheet arrangement is the same, except opposite hand, atthe right end. Thus the header end assemblies and 10 are at the ends ofthe conical shell end sections 21-21; and include the tube sheets 16,17, 16', 17 and the detector space barrels 18, 18.

End chambers 24, 24 formed within vthe vrespective headers communicatewith each other through a plurality of similar tubes 25 which are theinner tubes of the improved double tube construction. These inner tubes25 are closely surrounded with eicient metal to metal heat transfercontact by outer tubes 26. The inner and outer tubes 25 and 26 are bowedto one side as seen in Fig. 1, to permit differential expansion of thetubes with respect to shell 23, in operation, as is usual in theconstruction of bowed tube heat exchangers.

The tubes 25-26 are supported, while allowing for free sliding in thehorizontal direction, by a plurality of support rings 27 provided withinthe shell 23. Each support ring 27 includes a plurality of horizontalsupport surfaces formed by transverse support slats 28 (see Figs. 2 and4) so that the tubes are free to bow to a greater or lesser extent bysliding horizontally on the slats 28.

As is conventional in this general type of heat exchanger, the tlow ofheating medium in the tubes is indicated by arrows 29 in one directionand the ow of heated medium in the shell around the tubes is indicatedby arrows 30 from the ends of the shell toward the central portionthereof. With the directions of ow of heating and heated fluids as shownin the drawings the fluid within the tubes 25 flows from inlet member 32to inlet header chamber 24, then through tubes 25 to outlet headerchamber 24 then out through outlet member 32. The inlet and outletmembers 32 and 32 are connected in a usual manner with a source of and apoint of discharge for the heating medium. The fluid to be heatedpassing around the tubes 25-26 and within the shell 23 as indicated bythe directional arrows 30 enters the shell through a pair of inletconduits 33 and leaves the shell through a pair of outlet conduits 34,the conduits 33 and 34 having connections, not shown, with a source ofand a discharge for heated medium.

The leakage interceptor spaces 19 and 19 are each provided with a seriesof ports 35 formed of pipe sections 36 and caps 37 welded to each otherand to the ring barrels i8 or 18. One of the upper ports 35a may beprovided with a vent 38 and one of the lower ports 35b may be providedwith a drain 39. The other upper, lower and side ports 35 (Fig. 3) mayserve as inspection ports, being equipped with sight glasses if desired.

In Figs. l and 2, the head covers 12-12 are shown secured to therespective head flanges over sealing means including diaphragms 41welded inside of flanges 14 beyond grooves 42. This head closureconstruction forms no part of the present invention, being described andclaimed in co-pending Frank Boni, Jr., application Serial No. 337,324,tiled February 17, 1953.

Sections 21 and 21 have been referred to as somewhat conical because,referring to Fig. l, to accommodate the bowed tubes, shell 23 is oitcenter in a horizontal plane with respect to the leakage detector spaces19 and 19 which in turn are off center with respect to the headers 10and 10. And in Fig. 2 the shell 23 is olf center in a vertical planewith respect to the leakage detector spaces and headers. Thisarrangement is also shown in Fig. 3 which is an enlarged end view takenfrom the left end of the heat exchanger as viewed in Figs. 1 and 2.

It is .to be understood that for purposes of simplicity only some of thetubes havebeen shown in the drawings. However, a usual complete `tubebundle, as is well known in the art, extends between the tube sheets 16`and,.17 and 17 and 16. In Fig. 1, portions of only three double tubes25-26 are shown and portions of only two double tubes are shown in Fig.2. Only a portion of the complete number of tubes in the tube bundle isshown in Fig. 4. .It will be apparent from Fig. 4 that the support rings27 carrying the cross slats 28 may be supported within the shell 23 by aplurality of circumferentially spaced shims 45 intervening between shell23 and ring 27 and each welded to each of these members. As shown inFigs. ,2 and-4 shell 23 may be supported by a plurality of transversebase supports 46 carrying a pair of longitudinally extending bars 47with fillet welds 48 connecting the longitudinal bars to the transversebars andthe bars 47 t0 the shell 23.

In the Vbowed tube heat exchanger of Figs. 1 4, the ends of each tube ofeach double tube are mounted in tube sheets and ixedly secured therein.The headers are in communication with the inner passages in -the innertubes and the leakage detector spaces 19 and 19 are in communicationwith leakage detector passages between `the inner and outer tubes aswill be described.

Obviously the heat exchanger can be used for either heating or coolingbut for purposes of explanation the heat exchanger of Fig. 1 may be asteam generator with a molten metal or salt used as the heating mediumand flowing through tubes 25, and water to be converted 'into steam, theheated medium, passing through the shell 23. This can otherwise bedescribed as the molten metal being the medium to be cooled and thewater in the shell the Acooling medium.

Thus the cooling medium may be introduced through the inlets 33, andpasses in the direction of arrows 30 within the shell 23 around theouter tubes 26 of the double tubes 25-26 and then discharges throughoutlets 34 as steam. With the arrangement described, the medium to becooled, which may be a molten metal or salt enters through inlet 32 andpasses in the direction of arrows 29 into chamber 24 of header 10 andthrough the inner tubes 25 of the double tube assemblies to the otherend, then into chamber 24 of header 10', and out through the outlet 32'giving up its heat to the cooling water to convert the same to steam.

As previously stated, the double tube arrangement contemplates thepossible passage of a high temperature, or high pressure, or highlycorrosive molten metal or salt through the inner tubes 25 necessitatingthat they be made of a material which is strong and corrosion resistantat high temperature. Similarly the outer tubes should be formed of asimilar material. Such material may be, for example, stainless steel ornickel. With small diameter, thin-walled tubes of such materials formedin long lengths, it has been diicult if not impossible to form groovesin either the inside of the outer tubes or the outside of the innertubes to provide passages for the detection and collection of leakage inthe event of tube failure.

We have solved these diiculties, and provided other new and usefulresults associated with greater metal to metal contact between theconcentric tubes, greater ease of manufacture, greater variety ofmaterials which can be used for each of the tubes of the double tubeconstruction, and relatively greater ease of employing thinner walledtubes, by providing a relatively large number of relatively smalldimensioned grooves in the outer surface of the inner tubes.

In accordance with the present invention, grooves are formed on theoutside of the inner tube 25 by a rolling procedure similar to knurling.The rolling procedure is illustrated somewhat diagrammatically in Fig. 7wherein a tube 25 is shown with grooves 51 being impressed in the outersurfacep52 ofthe tube, starting from a zone 52a forming tool 53 isforced or pressed radially against the l tube surface 52 during suchrotation.

The roll 53 has axially extending ribs54 formed on its peripherycomplementary in cross-sectional shape to the shape of the grooves to beformed; and the roll rotates by pressure contact with the rotating tube.Assuming that the tube is rotated in a lathe-like machine, then afterone revolution of the tube with the tool pressed thereagainst at thezone 52a, the tool is fed axially along the tube to roll groove portions51a in the surface of the tube 25 in a helical path indicated by dotdash lines in Fig. 7, at 55, which line 55 shows the path traversed bythe left hand end of roll 53 as it is fed and the tube 25 rotated. f

The tube may be supported during rolling in any well known manner, ifnecessary, depending on its diameter, length and wall thickness. Thusthe tube may be supported on an arbor or mandrel; or back up rolls maysupport the tube opposite the location of roll pressure.

Alternately, the roll may be stationary and the tube fed axially fromthe head of an automatic screw machinelike machine for advancing thetube axially in a helical path past the roll.

The spacing of the ribs 54 on the roll 53, the axial length of the roll53, and the rate of relative advance between the tube and roll arecoordinated such that when the tube makes one revolution the grooveportions 51a formed in the helical path 55 are aligned with previouslyformed groove portions. As a result, when the rolling has progressed toadjacent the other end of the tube, a series of longitudinally extendinggrooves 51 are formed in the outer surface 52 of the tube 25.

The shape of the grooves 51 is shown somewhat dia grammatically and inan exaggerated manner in the enlarged sectional view of Fig. 6. Forexample the inner tube 25 may have a 5A: inch outside diameter, theouter tube 26 a 3%: inch outside diameter and the wall thickness of eachtube 25 and 26 may be 1A@ inch. The grooves 51 may only be a fewthousandths of an inch in depth or width and may have any desiredspacing to provide a relatively large number of grooves. Thecrosssectional contour of the grooves 51 is not critical as it may berounded, as shown, or fiat sided.

It is possible to form the grooves 51 in the surface of a stainlesssteel or nickel tube without distorting the tube or weakening the tubewall by large sized grooves, because the grooves are small in size andonly localized pressure by the roll against the tube occurs at the pointof Contact therebetween. On the other hand, it is not possible to formsuch grooves in the surface of such tubes, when made of stainless steelor nickel or the like, by extruding, broaching or machining, atreasonable cost or without substantially heavier walls,

Thus it is possible to use either nickel or stainless steel for bothinner and outer tubes or to have either made of either stainless steelor nickel, thereby affording a new design freedom in the design of heatexchangers of the type described. This method of forming grooves in theouter periphery of a round but very hard thin walled tube isparticularly advantageous because it is fast while at the same time nogreat forces are required for the operation beca-use the tool may bemade quite short and it is forced against the tube surface the fulldepth of only one very small groove at any one time.

After the grooves 51 have been formed in the outer surface of the tube25, the tube elements are ready for assembly in the heat exchanger. Theouter tubes 26 are first assembled within the shell 23 with the endsthereof seated in the tube sheets 17 and 17. The manner in which tubeends are secured within openings in tube sheets is well known `in theart and may include slightly 8 expanding the tube ends within the tubesheet openings, or welding the tube ends to the tube sheet, or both.

After the outer tubes 26 have been thus assembled, the grooved innertubes 25 are telescoped through the outer tubes with the groovedportions extending slightly beyond the outer ends of the outer tubes 26as shown at 52b in Fig. 5; and the ends of the inner tubes 25 are thenxedly secured in the tube sheets 16 and 16 by expanding or expanding andwelding the same within or to the tube sheets in the usual manner.Before both tube ends are secured to the tube sheets 16 and 16 anexpanding tool is moved through the inner tubes 25 to slightly expandthe inner tubes 25 within the outer tubes 26 to seat the inner tubesurfaces between the grooves in intimate metal to metal contact withinthe outer tubes so that for heat transfer purposes the thus formeddouble tubes act as single members to provide eicient heat transfer fromthe inner surfaces of the inner tubes to the outer surfaces of the outertubes.

The assembly of the double tubes 25-26 with the tube sheets may bemodified by rst telescoping the tubes 25 Within tubes 26 with one end oftube 26 beyond an end of tube 25. Such tube end of tube 26 is thenexpanded within its tube sheet opening and welded thereto if desired.Then tube 25 is moved axially of tube 26 to permit the other end of tube26 to be expanded, and welded in its tube sheet opening. Then one end oftube 25 is expanded, and welded if desired in its tube sheet opening.Then an expanding tool is drawn through inner tube 25 to expand its walloutward into intimate metal to metal heat transfer contact Within outertube 26. Finally the other end of inner tube 25 is expanded in, andwelded if desired in its tube sheet opening.

As shown in Fig. 3, each head cover 12 may be provided with a liftingeye 49 `for use in handling the heat exchanger during manufacture,shipment, installation and repair, or for removal of the head cover ifnecessary to replace one or more tubes.

As best shown in Fig. 5, the grooves 51 provide passages throughout theentire length of the double tubes between the inner and outer tubes 25and 26 thereof communicating with the leakage detector chambers 19 and19. In the event of a failure of any of the tubes 25 or 26, leakage offluid through the failing tube will pass along grooves 51 to thechambers 19 and 19' where such leakage may be visible through inspectionopenings in detector ports 35 or from drains 39 in lower ports 35h. Whenany such leakage is detected, the heat exchanger may be shut down, thetube failure located and the tube replaced in the usual manner.

Thus by providing for leakage detection indicating tube failure, andcorrecting the same when detected, intermixing of the heating and heatedor cooling and cooled liquids or uids may be prevented.

Although in Figs. l and 2 the leakage detector compartments 19 and 19are shown as separate compartments, in some installations the barrels`18 and 18 may be omitted and the passages between the inner and outertubes of the double tubes 25 and 26 may communicate directly with theatmosphere where any tube leakage will be immediately detected.

Furthermore, if desired, a third liquid or uid may be introduced intothe leakage detector spaces 19 and 19 and circulated through thepassages formed by the grooves 51 between the inner and outer tubes 25and 26.

A modified groove forming roll arrangement is shown in Fig. 7a in whichthe grooves 51 may be formed longitudinally in the outer surface of tube25 by a forming roll 53a having helical ribs 54a thereon and with theroll axis angled with respect to the axis on which tube 25 is rotated.The roll 53a is forced against tube 25 with pressure and moved axiallyof tube 25 during tube rotation to form grooves 51 in substantially thesame manner as described in connection with Fig. 7, except that at anyone moment there is less rib area contact with the tube n.Surfacenermitting highiloealized forming pressure to he exerted by roll '53a:against the :..resistanee-of hard, tough metal Such as stainless steelor niekel.

AA bayonet .tube .heat v-exeluanger is shown inligs. 8 ,and 9 ,including`:the improved double tube construction made in accordance with thepresent invention. T he bayonet tube heat exchanger indicated at 100 hasa `main header 110 similar to the header 10 and may the equipped With aI head COVeIBuddiaphragmlhead `closure, not shown, .Similar t the headCover 'andclosure in the heat exchanger shown rin vFigp1.

The header 110 preferably comprises .a barrel portion l1,1 1 secured by,an annular ,weld 11:5 .to tube :sheet '.116 spaced Afrom la second tube,sheet 117 by ring barrel 118 Welded .t0 the tube sheetsglland 11.7 toform a leakage deteCOr Space 11,9. Tube .Sheetg1'17 is connected by anannular weld 120 with heatexchanged shell 123, ,the other lend of theshell being closed by :a .dome 210 secured `by a weld 220.

In the construction ,of a bayonet tube heat exchanger, the inlet andoutlet 'for the tube passages normallyare `at one end of the unit whichmay be the stationary end thereof and the :tubesandshellsare constructedto provide lfor relative differential longitudinal expansion andvcontraction.

A sealing ring 121 preferably is welded within the periphery of barrelportion 111 intermediate its V.ends and a series of nuts 1,22 are weldedto .the sealing ring 121, to which studs `124 are secured for mounting.a pass plate 127 within the barrel portion 111 by nuts 128. The barrelportion 111 is thus divided intov two compartments 129 and 130, and atube fluid inlet 131 and a tube fluid outlet 132 may communicaterespectively with the compartments 129 4and 130.

The improved double Ytube vconstruction including inner tubes 125 andou-ter -tubes -1'26 is mounted within the shell 123 with one end of eachVofthe outer tubes '126xed in the tube sheet 117 and one end of eachof'the inner tubes 125 xed in the tube sheet 1 16, ferrules 133preferably being provided for seating the ends of the inner tubes intube sheet '116. Bayonet tubes 134 are mounted at one end in pass plate127 and project, as shown, inside of the inner tubes 125, the open endsthereof preferably being supported by spacers 135. The unsecured ends ofthe double tubes 125-126 may be closed by return plugs 136 and 137welded thereto.

Thus tube fluid may be pressed through the tubes through the inlet 131,compartment 129, the bayonet tubes 134 to the open ends thereof, thenback around the outer surface of the bayonet tubes 134 and within theinterior of the inner tubes 125 to compartment 130 and out throughoutlet 132.

The inner tubes 125 of the improved double tube construction 125-126 areprovided exteriorly with grooves in a manner previously described sothat passages are provided by such grooves between the inner and outertubes 125 and 126 communicating with leakage detector compartment 119 ina manner previously described.

Compartment 119 may be equipped with an inspection port 138 and a lowerport 139 having a drain connection 140 for discharging any liquidleakage, thus indicating tube failure. A series of baflles 141 aremounted within the shell 123 on tie rods 142 between spacers 143, thetie rods 142 being secured to tube sheet 117 at one end and to the lastbaille 141 at the other end. Adjacent the tube sheet 117, one of thebaffles 141a has connected thereto a horizontal baille plate 144 whichenclose the cut-off upper ends of baffles 141b as well shown in Fig. 9.

The baffles 141, 141a and 141b are provided with openings 145 throughwhich the double tubes 125 and 126 project, clearance spaces beingprovided by said openings 145 around the double tubes so that fluidpassing through the shell can travel through such clearance spaces, asindicated by the arrows 146, from space to space be- Atitl-.een batllesin .close heating contact with ,the :outside-of .ticularly adapted `foruseasa superheater, with steam passing into the shell .at 147 and beingdischargedtherefrom through koutlet 148 as superheated steam, .thesuperheating being performed by the heating fluid circulated through thebayonet tubes 13.4 and double tubes and 126.

The shell 123 may be provided with any desired number of supportsincluding ,cross members 149 and longitudinal members 150 (Fig. 9)welded to each other and to the shellfor supporting :the vsame on .asupporting surface; and drain opening connections 151 .and `152 may beconnected with `compartment and ,the interior of shell L123 for drainingthese ycompartments when necessary.

Accordingly, the present invention provides a new meth- .od of makingdouble tubes an'd =a new double tube structure which maybe used invario-us `types of heat exchangers as illustrated and described intheembodiments of the in- Vention disclosed. The Adouble tube constructionmay readily be manufactured to provide many small grooves in the outersurface of the inner tubes. Thin walled small diameter long length tubesmay be formed ofmetal .such kas stainless steel and nickel with ymany`resultant advantages such as maximum Vmetal to metal contact betweenthe inner ,and ,outer .tu-bes for efllcient heat transfer, greater easeof manufacture, greater design freedom from the standpoint of-metalsthat may be used to form .the tubes, elimination of a requirement thatsoft metals be used, and provision for the detection' of -lluidleakageAdue to tube failure and prevention of intermixing of shell and tubefluids.

Moreover, the improved method enables grooves to be formed in very thinwalled tubes with Va costsaving where expensive materials are used andwith a substantial weight reduction due to the ability of using thinwalled tubes.

The construction of the present invention also provides other importantand new advantages and results in that leakage warning may be givenwithout endangering personnel, an'd leakage location determined withoutdifficulty.

Thus, referring to Fig. 1, the leakage detector spaces 19 and 19 and thepassages provided by grooves 51 may be filled with a fluid underpressure such as helium, air, water or mercury and sealed under suchpressure. Suitable instruments for indicating or recording the pressuremay be connected with one of the compartments 19 and 19. Duringoperation of `the equipment, if the pressure un'der which such fluid ismaintained in the compartments 19 and 19 and grooves 51 is a pressureintermediate the pressure within tubes 25 and outside fof tubes 26, andthe pressure within tube 25 is lower than the pressure outside of tubes26; then a decrease in the pressure of the fluid in compartment 19indicates leakage through tubes 25 or the joints thereof, and anincrease in pressure of the fluid in compartment 19 indicates leakagethrough tubes 26 or the joints thereof. A

If the pressure of such fluid in compartment 19 is maintained higherthan the pressure inside of tubes 25 and higher than the pressureoutside :of tubes 26, then a decrease in pressure of the fluid incompartment 19 shows leakage through one of tubes 25 or 26 or the jointsthereof. Similarly, if the pressure of the fluid in compartment 19 ismaintained lower than the pressure inside of tubes 25 and outside oftubes 26, then' an increase in the pressure of the fluid in compartment19 indicates leakage through tubes 25 Ior 26 or the joints thereof.

Thus, if either of the fluids in or around the tubes 25 or 26 is lethal,toxic, explosive, inflammable or dangerous, and leakage occurs throughone of tubes 25 or 26,

` the construction provides for leakage detection which may Moreover, ifany leakage does occur, the location of the leakage tube can be readilydetermined. When leakage is detected, the unit may be shut ol'l and headdiaphragm 41 removed. If the pressure change indication of fluid incompartment 19 indicates leakage in one or more of the tubes 25, thecompartment 19 may be pressurized, the outside ends of the tubes 25 intube sheet 15 may be covered in the usual manner with a solution' suchas a soap solution which will form bubbles from pressure leakage throughthe defective tube, and the location of the leak determined. The failingtube 25 can then be repaired.

lf the iluid pressure change in compartment 19 indi cates leakage in oneor more of tubes 26, `one or more of ports 35 or 35a may be opened andprovided with sight glasses, the shell 23 pressurized and thecompartment 19 slowly filled with water. As the water level in'compartment 19 rises, by observing through horizontal ports, thehorizontal location of the leaking tube 26 can -be observed throughbubbling in the water. At the same time, observation can be madevertically through one of the ports to determine the lateral location ofthe leaking tube. When the location of the leaking tube is thusdetermined, the 'tube can be repaired or blocked off in' the usualmanner.

In the foregoing description, certain terms have been used for brevity,clearness and understanding, but no unnecessary limitations are to beimplied therefrom beyond the requirements of the prior art, because suchwords are used for descriptive purposes herein an'd are intended to bebroadly construed.

Moreover, the embodiments of the improved construction and methodillustrated and described are by way of example, and the scope of thepresent invention is not limited to the exact details illustrated ordescribed.

Having now described the invention, the construction 12 and mode ofmanufacture of preferred embodiments thereof, and the advantageous, newand useful results obtained thereby; the new and useful arrangements,constructions, parts, elements, combinations, subcombinations, methods,steps, procedures, principles and discoveries, and reasonable mechanicalequivalents thereof obvious to those fskilled in the art are set forthin the appended claim.

Y We claim:

A small diameter, corrosion-resistant, double-walled leakage detectorheat exchanger tube having nearly complete metal to metal contactbetween the walls of the double-walled tube and being adapted forcontaining corrosive fluids at high temperatures including inner andouter cylindrical tubes of corrosion-resistant metal selected from theclass consisting of stainless steel and nickel, each of the inner andouter tubes having a wall thickness of the order of l/e thick, the outerdiameter of the outer tube being of the order of 1%" diameter, the innertube being provided with a plurality of longitudinally extending grooveshaving a width and depth of the order of a few thousandths of an inchformed into the cylindrical outer surface thereof, and the outercylinderical surface portions of the inner tube between the groovesbeing seated in intimate metal to metal heat transfer contact with theinn'er surface of the outer tube thereby providing metal to metalcontact between the inner and outer tubes greatly in excess of the totalprojected area of the few thousandths inch wide grooves whereby ecientheat transfer may be effected through .the walls of the double-walledtube.

References Cited in the tile of this patent UNITED STATES PATENTS1,589,595 Hitchcock June 22, 1926 1,842,945 Price et al. J an. 26, 19321,886,403 Jones Nov. 8, 1932 2,187,555 Flindt Jan. 16, 1940 2,658,728Evans Nov. l0, 1953 FOREIGN PATENTS 273,605 Great Britain July 12, 1927

